Organic wastes (water pollutants) dissolved in water systems, natural or synthetic, are decomposed and detoxified oxidatively by metabolic actions of aerobic microbes. Specifically, ammonia nitrogen mainly generated from the excretion of the aquatic life in the water systems is oxidized to nitrogen oxides such as nitrite nitrogen and nitrate nitrogen, and sulfurous and phosphorus organic wastes to sulfur- and phosphorus-based oxides such as sulfate and phosphate salts. However, accumulation of these oxides in water leads to decrease of pH and eutrophication, accelerating growth of algae and mosses, and thus causes deterioration in water quality, causing severe obstacles to long-term preservation of water quality.
On the other hand, when there is a poor-oxygen region in the aquatic system and when anaerobic microbes and an organic carbon source, energy for proliferation thereof, is present in the region, these oxides are decomposed in fermentation, i.e., reductive decomposition, by metabolism of the an aerobic microbes, and released into air, for example, as nitrogen gas.
The amount of the nitrogen-based wastes decomposed or eliminated biologically by the biological decomposition is known to depend roughly on the abundance ratio of carbon to nitrogen (C/N ratio). That is, the total nitrogen oxidized/reduced by microbial metabolism, in particular the decomposition rate of nitrogen oxides such as nitrite and nitrate nitrogens, is dependent on the organic carbon source concentration in the poor-oxygen region where the anaerobic microbes live. Generally, the C/N ratio most favorable to bring the microbial metabolism into the most active fermentation state is said to be 6 or more. It is thus quite important to add an organic carbon source deliberately for biological improvement in water quality.
A lower alcohol such as methanol or ethanol is commonly added as the organic carbon source, but, in such a case, supply of the liquid lower alcohol demands frequent and consistent addition of the alcohol, and also a large-scale facility, because it is necessary to control the amount of alcohol, for prevention of the water pollution by excessive addition of alcohol. In addition, methanol, when used, demands consideration of its adverse effect on the body, and it is necessary to pay significant attention, especially when an individual uses it at home.
To solve the problems associated with the use of a liquid organic carbon source, for example, Japanese Patent Application Laid-Open No. 9-234493 describes a method of adding a porous base material containing a mixture of a low-molecular weight sugar and a polysaccharide as organic carbon source for water treatment, while Japanese Patent Application Laid-Open No. 2001-269699 describes a method of using a starch-derived biodegradable plastic carrier as the organic carbon source for water treatment.